Regarding a semiconductor device utilizing a diamond substrate, JP-A 8-88235 discloses a field-effect transistor comprising, as provided on the surface of a hydrogen-terminated homoepitaxial diamond substrate of which the surface is terminated with hydrogen atoms, a source electrode and a drain electrode formed of gold, and a gate electrode made of aluminium. JP-A 2004-109020 discloses a p-channel field-effect transistor utilizing a liquid electrolyte as a gate and, as a channel, a diamond surface being comprised of a hydrogen termination and an oxygen termination as mixed therein through partial oxidation process of the hydrogen-terminated surface by ozone treatment.
In this type of semiconductor devices, the electric conductivity of the device shall be improved by terminating the interface between the electrode and the substrate by hydrogen, which makes it better the device performance.
However, in the conventional semiconductor devices, a hydrogen termination is formed also on the substrate surface where electrodes are not fabricated, leading to not only an electric conduction from the electrode to the diamond bulk via the diamond interface, but also electric conduction in the substrate surface between the electrodes, or that is, surface leakage current. The latter surface leakage current varies, greatly depending on the type and the amount of surface adsorbates, therefore destabilize the device performance. There is a problem that the performance destabilization is especially remarkable in severe environments such as high temperature device operation, etc.